The present invention relates to a noncontact power transmitting apparatus which can be used for portable communication equipment, such as a portable telephone and a PHS (personal handyphone system) telephone, various electrical apparatuses, electronic apparatuses, or the like which operate by using a rechargeable secondary battery as a power source. More particularly, the present invention concerns a noncontact power transmitting apparatus for transmitting electric power from a charging part to a part to be charged in a state of noncontact by means of the action of electromagnetic induction without via a metal contact.
Hereafter, a description will be given of a conventional device with reference to the drawings.
FIGS. 12A to 12C are explanatory diagrams illustrating a conventional charging device. FIG. 12A is a circuit diagram, FIG. 12B is a schematic diagram of coils, and FIG. 12C shows a B-H loop of a core. Hereafter, a description will be given of the conventional charging device with reference to FIGS. 12A to 12C. As an example of a noncontact power transmitting apparatus, an example of a dc power source apparatus disclosed in, for example, in Japanese Patent Publication JP 7-46841 is conventionally known. This apparatus is capable of realizing satisfactory regulation in a relatively wide output range, and has a circuit shown in FIGS. 12A to 12C, for instance. Hereafter, a description will be given of the operation of the circuit shown in FIGS. 12A to 12C.
A gate voltage of a field-effect transistor 7 is provided by the voltage which is charged in a first capacitor 2 from an output of a rectifying and smoothing circuit 1 through a first resistor 3. When the field-effect transistor 7 is turned on by the aforementioned voltage, a voltage is generated in a main winding 9 and a gate winding 10 of a primary transformer 8 in such a way that the sides marked with black dots become plus, so that the on-state of the field-effect transistor 7 is established.
Here, when the field-effect transistor 7 is turned on, because the electrical charge at the first capacitor 2 is discharged through a second resistor 4 and a first diode 5, the voltage at the first capacitor 2 declines and the field-effect transistor 7 is turned off after a certain time elapsed. When the field-effect transistor 7 is turned off, the first capacitor 2 is charged through the resistor 3, and when the voltage at the first capacitor 2 reaches a predetermined value, the field-effect transistor 7 is turned on. Thus, a primary circuit undergoes self-oscillation.
At this time, in the primary circuit, electric power is transmitted from the primary transformer 8 (power-transmitting coil portion), and this power is received by a secondary transformer 11 (power-receiving coil portion) of a secondary circuit. Then, current flows across a fourth capacitor 14 by the voltage induced in the secondary transformer 11, and the voltage is generated in the secondary circuit. The current is rectified by this voltage through a diode 12, and a capacitor 13 is charged to generate a dc voltage.
The primary transformer 8 (power-transmitting coil portion) and the secondary transformer 11 (power-receiving coil portion) are used in the relationship such as shown in FIG. 12B. In the above-described circuit, since the primary transformer 8 is driven by a single field-effect transistor 7 as the above-described manner, the magnetic flux of the core of the primary transformer 8 and the secondary transformer 11 is oscillated only in the first quadrant as shown by a B-H loop (B: magnetic flux density, H: magnetic field strength) in FIG. 12C. That is, the magnetic flux acts only on one upper or lower side of the B-H loop.
With the above-described conventional noncontact power transmitting apparatus, the following problems are encountered.
With the above-described conventional apparatus, the magnetic flux of the core of the primary transformer 8 (power-transmitting coil portion) and the secondary transformer 11 (power-receiving coil portion) is oscillated only in the first quadrant as shown by the B-H loop in FIG. 12C, and the magnetic flux acts only on one upper or lower side of the B-H loop. Accordingly, the efficiency in the noncontact power transmission is poor, so that in order to produce large power from the secondary transformer 11 (power-receiving coil portion), it is necessary to make the secondary transformer 11 large-sized, and the weight becomes heavy.
Further, with the above-described conventional apparatus, the magnetic path of the primary transformer 8 (power-transmitting coil portion) and the secondary transformer 11 (power-receiving coil portion) is configured such that the leakage flux is large, and effective use is not made of the magnetic flux generated by the primary transformer 8 (power-transmitting coil portion). For this reason, in order to produce large power (e.g., 5 W or more) from the secondary transformer 11 (power-receiving coil portion) so as to rapidly charge a large-capacity secondary battery, such as a lithium ion secondary battery, the secondary transformer 11 (power-receiving coil portion) becomes large-sized, and the weight becomes heavy.
In a case where the above-described conventional apparatus is used for a portable telephone, for example, the secondary transformer 11 (power-receiving coil portion) must be incorporated on portable telephone body side, while the primary transformer 8 (power-transmitting coil portion) must be incorporated on the charger side. Therefore, if the secondary transformer 11 (power-receiving coil portion) is large-sized and the weight is heavy as described above, the portable telephone body (handset), which needs to be always carried by a user, becomes large-sized and heavy, which is inconvenient.